1. Field of the Invention
The present invention generally relates to a lithographic apparatus and a method for manufacturing a device. More specifically, the invention relates to a system and method for synchronizing elements of a system for controlling the lithographic apparatus.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which can be referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern can be transferred onto all or part of the substrate (e.g., a glass plate), by imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate.
Instead of a circuit pattern, the patterning device can be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can be a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system. For example, a patterning device can flexibly alter the exposure region on a substrate to accommodate the manufacture of various shapes.
For instance, a flat panel display substrate is typically rectangular in shape. A lithographic apparatus designed to expose a substrate of this type can provide an exposure region that covers a full width of the rectangular substrate, or covers a portion of the width (for example half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through a beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
A lithographic apparatus will have a variety of subsystems and processes that need to be precisely synchronized. At a macro level, for instance, a projection system including a light source such as a laser beam, a patterning device, substrate stage and/or a patterning device stage must all be tightly synchronized in any specific application. At a finer level, the flow of data throughout the lithographic apparatus must be tightly synchronized to ensure that exposure periods are precisely aligned with the patterning device. This is especially true in optical maskless lithography (OML) lithographic tools that use the above mentioned patterning device that comprises an array of individually controllable elements. Such patterning devices typically have a plurality of controlling devices, drivers and data stores, all of which must remain tightly synchronized to maximize throughput and minimize errors.
Very accurate synchronization of multiple systems is difficult, especially if the parts of the lithographic apparatus are physically installed outside the actual fabrication room. For maskless systems, this is typically the case due to heat regulation issues, physical constraints and price per square meter in the clean room environment.